The present invention relates to a method for coupling a surface-oriented opto-electronic element with an optical fiber, and an opto-electronic element for carrying out such a method.
The coupling between an opto-electronic element or chip and an optical fiber, particularly, a monomode fiber, represents a complex problem because the two components must be aligned relative to one another to achieve a high coupling performance with high efficiency in the xcexcm or sub-xcexcm range. Prior art methods for producing a coupling include, on one hand, a coupling technique with lenses or other beam transforming elements, and on the other hand, direct techniques, referred to as butt coupling methods.
Generally, an optical fiber is aligned relative to an opto-electronic chip for purposes of achieving a high coupling performance by an active aligning technique, i.e., an experimental determination of the favorable positioning of the optical fiber and the opto-electronic chip. Active aligning is disadvantageously time consuming and cost-intensive.
Another prior art technique is what is referred to as passive alignment, which provides for the utilization of positioning aids that are provided at one of the coupling partners or at a coupling device. The positioning aids make possible a passive alignment between an opto-electronic chip and an optical fiber that is to be coupled therewith, but the provision of the positioning aids is associated with an additional outlay and additional costs.
It is accordingly an object of the invention to provide a method for coupling a surface-oriented opto-electronic element with an optical fiber and opto-electronic element for carrying out such a method that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that makes it possible to connect the two parts easily while providing a high coupling performance.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of coupling an element with a fiber, including the steps of providing an optical fiber having a fiber rotational axis and a fiber butt, providing a surface-oriented opto-electronic element having an optically active zone, a rotational axis, and a rotationally symmetric protruding structure symmetrically disposed with respect to the optically active zone, wetting at least one of the fiber butt and the protruding structure with a transparent adhesive, moving the element and the optical fiber toward each other to spread the adhesive therebetween, disposing at least one of the element and the fiber to enable a substantially frictionless movement of the fiber perpendicular to the rotational axis of the element and perpendicular to the fiber rotational axis, waiting for the fiber and the protruding portion to self-center, and one of waiting for and bringing about a hardening of the adhesive to fix the now-centered configuration between the fiber and the protruding portion.
Accordingly, it is inventively provided that, first, the butt of an optical fiber and/or a rotationally symmetric protruding structure of an opto-electronic element are wetted with a transparent adhesive. The rotationally symmetrical structure is constructed symmetrical to the optically active zone of the opto-electronic element. Next, the two elements that are to be coupled are moved toward each other, whereby the adhesive between the front side of the fiber and the protruding structure spreads. The opto-electronic element and/or the fiber are disposed so as to allow substantially frictionless movement perpendicular to the rotational axis of the opto-electronic element, i.e., perpendicular to the rotational axis of the fiber. Such a configuration makes possible an automatic positioning of the two coupling elements relative to one another. The element automatically positions itself relative to the optical fiber and vice-versa by virtue of the surface tension and the capillary effect of the adhesive.
A rotationally symmetrical structure in the sense of the invention is any structure that is projected on itself given rotation about at least one angle not equal to 360xc2x0. In other words, if there exists a line g and at least one angle a, such that the body is projected onto itself given rotation about the line g and the angle a, then the body is rotationally symmetric. In particular, this includes not only circular and annular structures but also polygons, particularly, triangles, quadrilaterals, pentagons, etc. Rotational symmetry in the sense of the invention is, thus, identified with a structure whose center of gravity is on center.
What is meant by substantially frictionless movement perpendicular to the axis of rotation of the opto-electronic element or perpendicular to the rotational axis of the fiber is movement that is opposed by such slight friction that there is no impediment to alignment based upon the surface tension and capillary effect of the adhesive. This is the case, particularly, with a floating configuration of the element. Specifically, a symmetrical configuration of the rotationally symmetric protruding structure relative to the optically active zone means that the protruding structure and the optically active zone have a common center of gravity (i.e., one situated on a common axis of rotation). The optically active zone is, preferably, also configured rotationally symmetrical.
Due to the rotational symmetry of the protruding structure, a positioning is achieved by bringing the rotational axis of the protruding structure into congruence with the rotational axis of the (likewise rotationally symmetric) optical fiber. Because the protruding structure is disposed symmetrical to the optically active zone of the opto-electronic element, and this is, therefore, concentrically aligned relative to the protruding structure, the rotational axis of the optically active zone becomes aligned precisely on the rotational axis of the optical fiber. Such alignment produces the highest possible coupling performance.
After the successful self-centering of the protruding portion, i.e., the optically active zone, and the optical fiber, the adhesive is hardened. Hardening can occur automatically with the passage of time, or, alternatively, by a separate curing aid such as UV irradiation. The ideal positioning between the two coupling partners is fixed in time and space by the curing of the adhesive. As a result, the optically active zone or surface of the opto-electronic element is aligned concentric to the fiber core and fixed there, which makes possible an optimal coupling.
Wetting with an adhesive may occur on the butt side of the fiber only, on the protruding structure of the opto-electronic component only, or on both.
In accordance with another mode of the invention, the opto-electronic element is placed on the butt of the (perpendicularly aligned) fiber and then released, i.e., separated from outside holding components.
The element is disposed such that it floats on the butt of the fiber with the aid of the transparent adhesive and is borne by the adhesive. The element can, therefore, be displaced perpendicular to the rotational axis of the optical fiber. The relatively light element now moves relative to the butt side of the fiber under the effect of the surface tension of the adhesive and positions itself concentrically to the axis of the fiber. Under the influence of the surface tension, the surfaces of the adhesive form minimum areas, whereby the element (i.e., its rotationally symmetric protruding structure) is automatically centered.
It should be noted that, on principle, the invention can also provide that the element be borne in a floating fashion at a certain distance from the butt of the fiber by a holding devicexe2x80x94which engages the lateral ends of the element, for examplexe2x80x94in that the adhesive already fills the intermediate space between the protruding structure or the fiber. Here, a movement of the element perpendicular to the rotational axis of the fiber is, likewise, possible due to the floating bearing so that a centered alignment of the element can occur under the influence of the surface tension. Such a solution makes sense particularly when the element is too heavy to be placed completely on the butt of the fiber; i.e., the adhesive would not be able to bear it due to its weight.
The protruding rotationally symmetric structure can take several forms. In accordance with a further mode of the invention, a mesa structure with a substantially planar surface is provided. The protruding structure can also advantageously be cylindrical because, in such a case, it has the same symmetry as in the fiber with which it is to be coupled. Furthermore, the protruding structure has a smaller diameter than the fiber to reliably guarantee a concentric centering. The opto-electronic element itself, preferably, has a diameter that corresponds to the diameter of the optical fiber or is larger or smaller by up to a factor of 2.
Alternatively, the protruding structure can also be formed by a ring structure, whereby the ring surrounds the optically active zone, containing it centrally. Likewise, the protruding structure can be an equilateral triangle, a square, a pentagon, or some other polygon.
In accordance with an added mode of the invention, the optical fiber has a flat butt. But an optical fiber with a curved butt can also be used as the optical fiber, whereby the butt acts to shape the beam (what is referred to as a lensed fiber).
In accordance with an additional mode of the invention, the coupling region between the fiber and the opto-electronic transducer and/or adjoining regions are coated with a casting compound. Such a configuration serves as protection against outside influences and provides additional mechanical stability.
The inventive surface-oriented opto-electronic element is characterized by a rotationally symmetric protruding structure that is formed at the element symmetrical to the optically active zone.
In accordance with yet another mode of the invention, the element is fastened to a PCB after being coupled with the fiber to face an optically active zone of the element towards the PCB and to avert the protruding structure from the PCB.
In accordance with yet a further mode of the invention, the element is fastened to a PCB after being coupled with the fiber to avert an optically active zone of the element and the protruding structure from the PCB.
In accordance with yet an added mode of the invention, the surface-oriented opto-electronic element is one of a VCSEL laser diode, an LED, and a photodiode.
With the objects of the invention in view, there is also provided an opto-electronic structure, including a surface-oriented opto-electronic element having a substrate with a surface region and an optically active zone formed at the surface region, and a rotationally symmetrical protruding structure connected to the substrate and symmetrically disposed with respect to the optically active zone.
In accordance with yet an additional feature of the invention, the optically active zone is formed in the surface region.
In accordance with again another feature of the invention, the protruding structure is formed at the surface region.
It falls within the scope of the invention either that the protruding structure is realized on the same surface as the optically active zone, or that the protruding structure is realized opposite the surface with the optically active zone.
In accordance with again a further feature of the invention, the optically active zone is formed at a given surface and the protruding structure is formed on the given surface.
In accordance with again an added feature of the invention, the substrate has an opposing surface opposite the surface region and the protruding structure is formed at the opposing surface.
In accordance with a concomitant feature of the invention, the substrate has a given surface and an opposing surface opposite the given surface, the optically active zone is formed at the given surface, and the protruding structure is formed on the opposing surface.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for coupling a surface-oriented opto-electronic element with an optical fiber and opto-electronic element for carrying out such a method, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.